This invention is directed to telephones and more particularly, to rotary dial or push-button types which complete a call by making desired connections at a telephone central office. For purposes of illustration, a push-button telephone will be referred to. However, the comments relate as well to a rotary (dial) type. With regard to the push-button type, by pressing and releasing a plurality of plungers on a numerical face plate on a telephone, a corresponding plurality of different tones or frequencies are respectively generated on the subscriber's line, the number called depending upon the tones created by the various plungers depressed and released. The electrical tones or frequencies thus generated are transmitted to the central office where they control the movement of an electromechanical device called a selector through which the subscriber's line is connected to other selective mechanisms. Each successive digit formed by the plungers produces another series of such tones which advance the call one step toward completion until the final operation occurs whereby connection is made to the called telephone.
The use of Touch Tone push-button telephones is being gradually extended in this country and in all parts of the world. Additionally, the Touch Tone telephones are so perfected that toll calls can be made directly by the caller or subscriber through new central station equipment. However, the subscriber may not authorize the caller to make such toll or local calls and thus he is charged for calls he knows nothing about.
Further, it is desirable to utilize the telephone to control incoming calls so that they can be switched to other necessary circuits if desired.